Preliminary Forecasts
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FXUS02 KWNH 260646
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 AM EDT SUN APR 26 2015

VALID 12Z WED APR 29 2015 - 12Z SUN MAY 03 2015

...OVERVIEW...

THE MAJORITY OF GUIDANCE CONTINUES TO SUGGEST THAT IN THE MEAN A
RIDGE SHOULD BUILD INTO THE CNTRL AND EVENTUALLY E-CNTRL CONUS
WHILE A TROUGH SETTLES ALONG OR A LITTLE INLAND FROM THE WEST
COAST AND AN ERN TROUGH TRACKS INTO THE WRN ATLC LATE.  MODELS AND
ENSEMBLES ARE STILL HAVING DIFFICULTY IN RESOLVING IMPORTANT ERN
TROUGH DETAILS AFFECTING WRN ATLC SFC EVOLUTION AS WELL AS
INDIVIDUAL SHRTWVS PASSING THROUGH THE WEST COAST TROUGH.


...GUIDANCE EVALUATION AND PREFERENCES...

CONTINUITY STILL APPEARS TO OFFER THE BEST COURSE OF ACTION
REGARDING THE EVOLUTION OF ERN CONUS UPR TROUGH EVOLUTION AND
ASSOC SFC LOW PRES TRACKING NEWD FROM OVER/NEAR THE FL PANHANDLE.
THERE ARE STILL SIGNIFICANT UNKNOWNS WITH RESPECT TO HOW LEADING
SHORT RANGE ENERGY EJECTING FROM THE PLAINS AND AMPLIFYING NRN
STREAM ENERGY WILL EVOLVE/INTERACT... AND ENOUGH SPREAD TO KEEP
CONFIDENCE IN ANY PARTICULAR SOLN BELOW AVG.  WHILE THE 00Z GFS IS
A TAD SLOWER IT HAS AT LEAST JOINED RECENT ECMWF AND UKMET RUNS IN
BRINGING A PRONOUNCED CORE OF UPR LVL ENERGY FROM THE GRTLKS
THROUGH THE MID ATLC.  THE 00Z GEFS MEAN HAS NOT ADJUSTED AS FAR
SWD WITH THIS BUNDLE OF ENERGY BUT IT HAS TRENDED IN THAT
DIRECTION RELATIVE TO PREVIOUS RUNS.  AT THE SFC RECENT ECMWF RUNS
HAD BEEN A LITTLE IN THE WRN/NWRN PART OF THE FULL SOLN ENVELOPE
INTO LATE THU BUT 00Z MODEL TRENDS THUS FAR ARE IN THAT DIRECTION.
 IN ADDITION AN EARLY LOOK AT THE NEW 00Z ECMWF SHOWS A WWD TREND
AS WELL TOWARD WHAT MAY FINALLY BE A SOMEWHAT IMPROVED GUIDANCE
CLUSTER.  THROUGH THE 12Z/18Z CYCLE A 70/30 BLEND OF THE 12Z ECMWF
MEAN/12Z ECMWF BEST REPRESENTED CONTINUITY THROUGH DAY 4 THU.  30
PCT WEIGHTING OF THE 18Z GEFS MEAN WAS INTRODUCED ALONG WITH THE
ECMWF MEAN/ECMWF STARTING 12Z FRI TO YIELD A BETTER COMPROMISE AND
TO ACCOUNT FOR CONSIDERATIONS UPSTREAM.

A FAIR AMOUNT OF SPREAD ALSO EXISTS FOR ENERGY ON THE EXTREME SWRN
PART OF THE ERN TROUGH.  THE ENSEMBLE MEANS PROVIDE A GOOD
CONSERVATIVE FCST THAT IS ALSO CONSISTENT WITH TELECONNECTIONS
RELATIVE TO THE CORE OF POSITIVE HGT ANOMALIES REACHING THE UPR
MIDWEST/UPR GRTLKS TOWARD THE END OF THE PERIOD.  THESE TELECONS
DID NOT SUPPORT THE SLOW MOVING UPR LOW DEPICTED IN 12Z/18Z GFS
RUNS.  THE 00Z GFS HAS TRENDED MORE OPEN/PROGRESSIVE WITH THIS
ENERGY.

WITHIN THE WEST COAST MEAN TROUGH... OPERATIONAL RUNS FROM 12Z
ONWARD HAVE BEEN SUGGESTING A DEFINED SHRTWV MAY APPROACH/REACH
THE PAC NW ON WED AND THEN BRUSH THE NRN ROCKIES/PLAINS OVER THE
FOLLOWING TWO DAYS.  WHILE THERE IS STILL CONSIDERABLE TIMING
SPREAD ENOUGH OF A SIGNAL SEEMS TO EXIST TO DEPICT AN ASSOC SFC
FEATURE TO A LITTLE GREATER EXTENT THAN SEEN IN THE MEANS.  THE
18Z GEFS MEAN ADJUSTED A LITTLE TOWARD THE OPERATIONAL IDEA VERSUS
THE 12Z CYCLE.  BLENDING EQUAL WEIGHTS OF THE 18Z GEFS MEAN/12Z
ECMWF SERVES TO ADJUST THE FCST PARTIALLY IN THE OPERATIONAL
DIRECTION BY DAY 5 FRI... KEEPING IN MIND THAT THE DOWNSTREAM
RIDGE MAY FAVOR LEANING AWAY FROM THE MORE AMPLIFIED SOLNS FOR ANY
SHRTWV REACHING THE NRN TIER BY FRI.

AFTER THAT TIME THE ENSEMBLE MEANS AND RECENT ECMWF RUNS GENERALLY
AGREE THAT UPSTREAM FLOW SHOULD REACH THE MEAN TROUGH POSN...
WHICH COMPARES WELL TO TELECONS RELATIVE TO THE DOWNSTREAM
POSITIVE HGT ANOMALIES.  THE 00Z GFS BECOMES OUT OF PHASE VERSUS
CONSENSUS WITH NRN STREAM FLOW BY THE LATTER HALF OF THE FCST.
THE 12Z ECMWF/ECMWF MEAN AND 18Z GEFS MEAN REMAIN THE MOST
REASONABLE SOLNS BY SAT-SUN.


...SENSIBLE WEATHER HIGHLIGHTS...

UNCERTAINTIES AT THE SFC AND ALOFT OVER THE ERN STATES/WRN ATLC
CONTINUE TO MAKE IT DIFFICULT TO RESOLVE EXACT COVERAGE AND
INTENSITY OF PCPN DURING THE PERIOD.  THIS SYSTEM SFC/ALOFT SHOULD
KEEP DAYTIME HIGHS ON THE COOL SIDE AROUND MIDWEEK BEFORE TEMPS
RECOVER TO WITHIN A FEW DEGS ON EITHER SIDE OF NORMAL BY THE
WEEKEND.  MEANWHILE EXPECT ONE OR MORE PERIODS OF PCPN FROM THE
PAC NW ACROSS PARTS OF THE NRN TIER IN ASSOC WITH SHRTWVS ALOFT
AND MEAN FRONTAL BNDRY.  ALSO EXPECT AN INCREASE IN ACTIVITY
FARTHER SWD ACROSS THE CNTRL/SRN ROCKIES BY LATE WEEK INTO THE
WEEKEND.  TEMPS SHOULD BE WELL ABOVE NORMAL FROM THE INTERIOR WEST
INTO THE NRN HALF OF THE PLAINS AS WELL AS EXTENDING INTO THE
MIDWEST/GRTLKS LATER IN THE PERIOD... WITH A DECENT AREA OF PLUS
10-20F ANOMALIES MOST DAYS.

RAUSCH

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